The present invention relates to a supercharger of an internal combustion engine.
A supercharger of an internal combustion engine comprises a compressor for pressurizing air. The pressurized air is supplied to each cylinder of the engine. Thus, the amount of air taken into the combustion chamber of the cylinder increases, increasing the engine output.
As to a supercharger, a turbocharger and a mechanical supercharger are known. According to the turbocharger, the energy of exhaust gas rotates the turbine. The turbine rotates a compressor. Such a turbocharger is disclosed in, for example, Japanese Patent Application Unexamined Publication (Kokai) No. 2002-317640. According to the mechanical supercharger, a driving shaft of an engine rotates a compressor.
A motor may be used for rotating the compressor. For example, a turbocharger may comprise a motor between the turbine and the compressor. When the volume of exhaust gas is low, the motor rotates the compressor. Such a turbocharger is disclosed in, for example, Japanese Patent Application Unexamined Publication (Kokai) No. H07-259576.
According to another example, the mechanical supercharger may comprise a motor. The driving force of an engine is converted into electric power, by which the motor is driven. The motor rotates the compressor. According to yet another example, a supercharger may comprise an oil hydraulic pump that is driven by the engine. The turbine is driven by high pressure oil. Such a supercharger is disclosed in, for example, Japanese Patent Application Unexamined Publication (Kokai) No. H08-200083.
Since the turbocharger utilizes the energy of exhaust gas, energy efficiency is high. However, the turbine provided in the exhaust system may cause a rise in the exhaust gas pressure. If the exhaust gas pressure is high when the engine load is high, an engine knocking tends to occur and a pumping loss may increase. When the engine load is low, the volume of exhaust gas decreases, which may lead to a shortage of the supercharged pressure. In some vehicles, control for quickly activating the catalyst by the heat of exhaust gas is performed. If the exhaust gas is used for driving the turbine, the time required for activating the catalyst may be long.
The turbocharger with a motor may solve the shortage of the supercharged pressure. However, the above problems regarding the rise in the exhaust gas pressure and the time required for activating the catalyst are not solved.
Since the mechanical supercharger utilizes rotation of a driving shaft of the engine, the supercharged pressure quickly responds to an engine driving force that is requested by the driver. Since a turbine does not need to be provided in the exhaust system, the time for activating the catalyst is appropriately maintained. However, since rotation of the driving shaft of the engine is required, a loss of the engine output (which is referred to as a “driving loss”) may occur in accordance with an increase in the amount of supercharged air.
According to the mechanical supercharger with a motor, the energy efficiency is low since the engine driving force is converted into electric power and then the electric power is converted into the motor driving force.
Thus, one object of the present invention is to provide a new supercharger that can overcome the above-described disadvantages of the turbocharger and the mechanical supercharger. Such a new supercharger can generate a desired engine output over a wide range of the engine rotational speed.